Field of the Invention
The present invention generally relates to a mobile communications technology, and more particularly, to a multiple user multiple input multiple output (MU MIMO) transmission technology.
Description of the Prior Art
In a Frequency Division Duplexing (FDD) system, downlink closed loop MIMO processing requires channel state information (CSI) feedback from a user equipment (UE). With the increase of the number of base station antennas, the feedback payload also increases, which makes it more and more difficult for the CSI feedback payload to meet the requirement of an actual application. In a large scale antenna system, a base station device may be equipped with and use 100 or more antennas. In this case, the conventional short-time CSI feedback is impractical for the actual application. In another aspect, the decrease of the total transmit power of the large scale antenna system mostly relies on precise CSI, which also makes the CSI feedback essential in the large scale antenna system.